1. Field of the Invention
The present invention relates to a control method for a hydraulic-driven winch for controlling rotation of a winch drum driven by a hydraulic motor, and apparatus therefor.
2. Description of the Related Art
Conventionally, a control apparatus for a hydraulic-driven winch is constituted, as shown in Japanese Patent Publication No. 63-35555 Publication, such that a clutch and both negative and positive brakes are provided on a winch drum, whereby
{circle around (1)} when the drum is driven, a brake is turned off and a clutch is turned on to transmit a rotational force of a hydraulic motor,
{circle around (2)} when the drum is stopping, the clutch is turned off and the brake is turned on to hold the drum in a stop state; and
{circle around (3)} in the free-fall state for freely falling a suspended load, both the clutch and the negative brake are turned off to make the winch drum free, and the drum""s rotational speed is adjusted by pedal operation of the positive brake while rotating the winch drum by the weight of the suspended load.
However, in the aforementioned conventional apparatus, the clutch, the positive brake and a control system for the former are necessary for the free-fall, and as a result, the apparatus constitution becomes complicated, and the cost increases.
Further, the conventional apparatus has a disadvantage that speed adjustment of the winch drum in the free fall is accomplished by a frictional brake (a positive brake), and as a result, the brake equipment becomes larger and heavier and control of abrasion of frictional parts is necessary, for which maintenance is cumbersome.
It is an object of the present invention to provide a control method for a hydraulic-driven winch for controlling rotation of a winch drum driven by a hydraulic motor, and apparatus therefor, which requires no clutch and brake for a free fall, and which is capable of securing an excellent operation feeling by the free-fall characteristic approximate to a mechanical brake for activating speed adjusting action while moving down a suspended load by the suspended load weight.
A control method for a hydraulic-driven winch according to the present invention comprises, in a hydraulic-driven winch comprising a winch drum, a variable capacity type hydraulic motor for driving the winch drum, a hydraulic pump whose hydraulic source is the hydraulic motor, and a control valve for controlling supply and discharge of pressure oil with respect to the hydraulic motor, operating said valve to the winding-down side in a state in which capacity of said hydraulic motor is set to a small capacity when said winch drum is rotated for winding down, and adjusting motor holding pressure to thereby wind-down rotate said drum at high speed and control rotational speed.
In this case, the hydraulic motor is wind-down rotated at high speed by the wind-down operation in a state in which the motor capacity is set to a small capacity to carry out the free fall operation. Therefore, the clutch, the positive brake and the control system therefor for the free fall are unnecessary. Moreover, this is a system in which the motor holding pressure is adjusted with respect to the motor load pressure determined by the suspended load weight to obtain the brake action, that is a system for regulating the brake force according to the magnitude of load. Therefore, the suspended load moving down characteristic in the free fall is approximate to the moving down characteristic according to the conventional mechanical brake, thus enabling securing excellent operation feeling.
Further, preferably, the motor capacity is set to a small capacity, and inlet pressure of the hydraulic motor is set to low pressure.
In this case, since the inlet pressure of motor is controlled in the partial operation, the free fall operation can be carried out without trouble also in a small load, and there is no possibility that the rotational speed of motor is so high that looseness or winding disturbance of a rope occurs. In addition, the inlet pressure of motor instead of pump pressure is controlled, and therefore, in the constitution in which a single pump is used in common to a hydraulic motor for a winch drum and the other actuator, as in the case where the constitution for controlling pump pressure is employed, there occurs no evil that variation of pump pressure influences on the operation of the other actuator.
Further, a control apparatus for a hydraulic-driven winch according to the present invention for realizing the above method comprises a winch drum, a variable capacity type hydraulic motor for driving the winch drum, a hydraulic pump as hydraulic source for the hydraulic motor, a control valve for controlling supply and discharge with respect to the hydraulic motor, a control valve operating means for operating the control valve, a motor capacity control means for controlling capacity of the hydraulic motor, a free fall instructing means for instructing a small motor capacity to the motor capacity control means, and a motor holding pressure control means for controlling motor holding pressure in wind-down rotation of the hydraulic motor.
Further, preferably, the motor holding pressure control means is operatively connected to operation of the motor capacity control means according to the instructions from the free fall instructing means.
Further, preferably, there is provided a motor inlet pressure control valve for controlling inlet pressure of the hydraulic motor in the wind-down rotation of the winch drum.
Further, preferably, the motor inlet pressure control valve is operatively connected to operation of the motor capacity control means according to instructions from the free fall instructions means to control the motor inlet pressure.
Further, preferably, a variable relief valve is connected to a damper chamber of a counterbalance valve provided in a wind-up side pipeline of the hydraulic motor, and relief pressure of the variable relief valve is set to be low when the hydraulic motor begins to actuate, and to be high during rotation.
Further, preferably, a hydraulic pilot type relief valve is used as the variable relief valve, and motor inlet pressure is taken out and guided to pilot port of the variable relief valve whereby relief pressure of the variable relief valve is set to be low at the time of high pressure corresponding to the beginning of actuation of motor, and to be high at the time of low pressure corresponding to the during rotation of motor.
Further, preferably, a hydraulic pilot type relief valve is used as the variable relief valve, pressure corresponding to the operating amount of the control valve to the wind-down side is taken out and guided to the pilot port of the variable relief valve whereby relief pressure of the variable relief valve is set to be low when the operating amount is small, and to be high when the operating amount is large.
In this case, a variable relief valve is connected to a damper chamber of a counterbalance valve, and relief pressure (damper pressure) of the variable relief valve is set to be low when the hydraulic motor begins to actuate and to be high during rotation, that is, the relief pressure is set according to the motor inlet pressure or the operating amount. Therefore, it is possible to prevent occurrence of hunting while in the beginning of actuation, rising a pressure difference between a pilot pressure chamber of the counterbalance valve and the damper chamber to improve respondence, and lowering the pressure difference during rotation of motor.
Further, preferably, a restrictor is provided parallel to the motor inlet pressure control valve.
In this case, it is possible to suppress variation of motor inlet pressure small by the restrictor.
Further, preferably, a flow-rate control valve for limiting motor flow-rate less than discharge flow-rate of hydraulic pump is provided in a motor wind-up side pipeline.
In this case, the motor flow-rate can be limited less than the pump discharge flow-rate by the flow-rate control valve provided in the motor wind-up side pipeline (a motor outlet side pipeline when the free fall is operated). Because of this, even if the damper effect is deteriorated, it is possible to prevent hunting, and to be compatible the respondence with the stability.
Further, preferably, there is provided a wind-up side pressure detection means for detecting pressure of the wind-up side pipeline of the hydraulic motor, and the motor capacity control means increases the motor capacity as wind-up side pipeline pressure detected by the wind-up side pressure detection means is higher.
In this case, when in the free fall, load is great and pressure on the motor wind-up side is high, that is, where motor rotational speed is excessively high, since the wind-up side pressure is detected to increase the motor capacity, the motor rotational speed automatically lowers.
Further, preferably, as the motor capacity control means, an actuator for regulating motor capacity for varying capacity of the hydraulic motor, and an actuator control valve for actuating the actuator are provided, and as the free fall instructions means, a free fall valve for actuating the actuator between a large motor capacity position and a small motor capacity position through the actuator control valve.
Further, preferably, as the control valve, a hydraulic pilot type switching valve is used, and as the control valve operating means, a wind up side and wind down side remote control valve for supplying pilot pressure to the hydraulic pilot type switching valve is used, the free fall valve being connected to a pilot pressure line of the wind-down side remote control valve through a high pressure selection valve.
In this case, when the free fall valve is operated, the motor capacity is set to small capacity, and at the same time, the control valve is switched to the wind-down side. That is, the free fall operation is carried out merely by operation of the free fall valve. Therefore, as compared with the case where operation of the control valve to the wind-down side and switching of the motor capacity are separately carried out, the free fall operation is simple to prevent erroneous operation.
Furthermore, preferably, as the control valve, a hydraulic pilot type switching valve is used, and as the control valve operating means, a windup side and wind-down side remote control valve for supplying pilot pressure to the hydraulic pilot type switching valve is used, and a switching valve switched between a position for controlling only the control valve and a position for controlling both the control valve and the actuator is provided in the pilot pressure line of the wind-down side remote control valve so that the wind-down side remote control valve serves as the free fall valve.
In this case, since the wind-down remote control valve serves as the free fall valve, the whole cost can be suppressed.